This PDF file contains the front matter associated with SPIE Proceedings Volume 8434, including the Title Page, Copyright Information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We investigate the soliton pattern formation in an erbium-doped figure-of-eight double-clad fiber laser. The mode-locking is realized with a nonlinear amplifying loop mirror. Different soliton complexes have been obtained similar to those obtained when the mode-locking is achieved through the nonlinear polarization rotation technique.

We derive a new model to simulate passively Q-switched intracavity frequency-doubling solid-state laser. By introducing a nonlinear loss term caused by frequency-doubling crystal into the rate equations ,we can express the effect of second-harmonic generation (SHG). We apply a finite volume discretization on gain medium, saturable absorber and frequency-doubling crystal. "Dynamic Multimode Analysis (DMA)" and several Gaussian modes are utilized. At the end, numerical results of passively Q-switched intracavity frequency-doubling solid-state laser are presented. In the case of large pump radius,chaoic phenomenon can be observed numerically. In order to realize the 3D simulation, we mainly use two technics: One is that common rate equations are extended to a set of 3D multimode rate equations, which calculate photon number for different modes separately. The other is to take into account a finite volume discretization.

We demonstrate a high-power fiber-laser-based source of continuous-wave (cw), linearly-polarized radiation at 970 nm in a simple, compact, and practical design. Using direct single-pass second-harmonic-generation (SP-SHG) of a cw thulium fiber laser at 1940 nm in a 40-mm-long periodically-poled LiNbO₃ (PPLN) crystal, we have generated 13.1 W of output power at 970 nm for a fundamental power of 40 W. We achieved conversion efficiency as high as 32.7%. The generated second-harmonic output exhibits a passive power stability better than 1.4% (1σ value) over 1 hour, has a linewidth better than 0.3 nm, and a TEM₀₀ spatial beam profile with M²<1.6. We further performed relevant theoretical calculations for the characterization of SP-SHG in the crystal.

Starting from the propagation equations describing four-wave-mixing-basedwavelength conversion, we investigate how the conversion efficiency in silicon waveguides is influenced by the frequency difference between the pump and Stokes input waves. By means of numerical simulations we show that, by detuning this frequency difference slightly away from Raman resonance, the conversion efficiency does not necessarily decrease, but can even be more than doubled as compared to Raman-resonant operation. At the same time, other values of the frequency detuning that still remain well within the Raman linewidth can lead to a more than 10 dB decrease in efficiency. As such, we show that a high-resolution tuning of the frequency difference is not only necessary to obtain an optimal conversion efficiency, but also to avoid the detrimental efficiency decrease in case of an inadequate detuning. Finally, we discuss how the pump-Stokes frequency difference that is optimal for wavelength conversion varies with the length of the waveguide and with its dispersion characteristics.

In this paper I present a generic model that describes the lasing characteristics of continuous-wave circular and racetrack-shaped ring Raman lasers based on micro- and nano-scale silicon waveguides, including their lasing directionality and polarization behavior. This model explicitly takes into account the effective Raman gain values for forward and backward lasing, the Raman amplification in the bus waveguide, and the spatial gain variations for different polarization states in the ring structure. I show numerically that ring lasers based on micro-scale waveguides generate unidirectional lasing in either the forward or backward direction because of an asymmetry in nonlinear losses at near-infrared telecommunication wavelengths, whereas those based on nanowires yield only backward lasing due to a non-reciprocity in effective gain. Furthermore, the model indicates that backward lasing can yield a significantly higher lasing output at the bus waveguide facets than lasing in the forward direction. Finally, considering a TE-polarized pump input for a (100) grown silicon ring Raman laser, I demonstrate numerically that the polarization state of the lasing radiation strongly depends on whether micro-scale or nano-scale waveguides are used.

We present a generic approach to determine the phase mismatch for any optical nonlinear process. When applying this approach, which is based on the evaluation of local phase changes, to Raman- and Kerr-based four-wave-mixing in silicon waveguides, we obtain a novel expression for the phase mismatch which is more accurate as compared to the conventional definition; and which contains additional contributions due to the dispersion of the four-wave-mixing processes, the so-called four-wave-mixing dispersion. By means of numerical simulations, we show that this additional dispersion has a significant impact on the evolution of the phase mismatch along the waveguide, and thus on the conversion efficiency.

We design tellurite tapered photonic crystal fibers (PCFs) for broadband mid-infrared supercontinuum (SC) generation in the few-optical-cycle regime. We show that we can move the zero dispersion wavelength (ZDW) beyond 2 μm toward mid-IR wavelength region by tapering tellurite PCFs. We demonstrate the generation of sub-two-cycle soliton selfcompressed pulses from 200 fs to 19.1 fs and show more than one octave-spanning coherent SC, extending from 1675 to 3950 nm, generated in 8 mm-long tapered tellurite PCF with low input pulse energy of 1 nJ at 2.9 μm.

We report a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric oscillator (OPO). The technique is based on the deployment of an electro-optic phase modulator (EOM) in combination with an antiresonant ring (ARR) interferometer internal to a cw OPO. The scheme is implemented in a doubly-resonant cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm by a cw laser. With careful adjustment of the cavity length, modulation frequency and modulation depth, under different conditions, we achieved stable train of 730 ps and 450 ps pulses at a repetition rate of 160 MHz and 80 MHz, respectively. At degeneracy, spectral broadening of ~38 nm and ~20 nm has been observed corresponding to pulses of 160 MHz and 80 MHz repetition rate, respectively. We have confirmed true mode-locked operation by verifying ~4 times enhancement in second-harmonic-generation power under mode-locked operation at both 160 MHz and 80 MHz, compared to that in cw operation, for a fixed average fundamental power.

We demonstrate the use of an antiresonant ring (ARR) interferometer for optimum output coupling in a continuous-wave singly-resonant optical parametric oscillator (SRO). The cw SRO, based on a 50-mm-long MgO:PPLN crystal in a standing-wave cavity, is pumped by cw Ytterbium fiber laser at 1064 nm. The ARR interferometer is integrated into one arm of the SRO cavity. By fine adjustment of the ARR transmission, a continuously variable signal output coupling from 0.8% to 7.3% has been achieved, resulting in an optimum output coupling of ~4.6% for 23.2 W of input pump power. At this output coupling, the SRO provides 2.28 W of signal, together with 2.95 W of idler, for 23.2 W of pump power. We also show that the deployment of the ARR does not lead to any degradation in the output beam quality from the cw SRO. The technique provides a proof-of-principle demonstration to determine the absolute output coupling in cw SRO for which output power and extraction efficiency can be maximized.

We report a tunable, high-energy, single-pass, optical parametric generator (OPG) based on the new nonlinear material, cadmium silicon phosphide, CdSiP₂. The OPG is pumped by a laboratory designed cavity-dumped passively mode-locked, diode-pumped, Nd:YAG oscillator, providing 25 μJ pulses in 20 ps at 5 Hz. The pump energy is further boosted by a flashlamp-pumped Nd:YAG amplifier to 2.5 mJ. The OPG is temperature tunable over 1263-1286 nm (23 nm) in the signal and 6153-6731 nm (578 nm) in the idler, corresponding to a total tuning range of 601 nm. Using the single-pass OPG configuration, we have generated signal energy as high as 636 μJ at 1283 nm, together with an idler energy of 33 μJ at 6234 nm, for 2.1 mJ of input pump energy. The signal pulses generated from the OPG have a Gaussian pulse duration of 24 ps and an FWHM spectral bandwidth of 10.4 nm at central wavelength of 1276 nm. The corresponding idler spectrum has an FWHM bandwidth of 140 nm centered at 6404 nm.

We consider spatial hysteresis and modulational instability in arrays of nonlinear metallic nanoparticles. We show that such plasmonic systems are characterized by a bistable response, and they can support the propagation of dissipative switching waves (or plasmonic kinks) connecting the states with different polarization. We demonstrate that modulational instability, also inherent in our system, can lead to the formation of regular periodic or quasi-periodic modulations of the polarization. We reveal that arrays of metallic nanoparticles can support nonlinear localized modes of two different types - plasmon-solitons and plasmon-oscillons. They both possess deeply subwavelength size. However, the profile of plasmon-solitons is stationary; whereas plasmon-oscillons has the oscillating profile which can stand at rest or slowly drift along the chain.

This paper will review the current understanding of the so called nonlinear Shannon limit, and will speculate on methods to approach the limit through new system configurations, and increase the limit using new optical fibres.

Transmitting ultra-high symbol rate optical signals remains a challenge due to their high sensitivity to fluctuations of GVD and higher orders of dispersion in the transmission link. Being able to cancel the impairments due to those fluctuations is a key requirement to make transmission of ultrashort optical pulses practical. We demonstrate an automatic compensation scheme able to keep an Optical Time Division Multiplexed (OTDM) signal stable at a bandwidth of up to 1.28 Tbaud in spite of external perturbations. Our approach is based on monitoring the signal with a photonic-chip-based all-optical RF-spectrum analyzer. The measurement of a single parameter extracted from the RF-spectrum is used to drive a multidimensional optimization algorithm. We apply the method to the real time simultaneous compensation for 2^nd, 3^rd and 4^th order dispersion using an LCOS spectral pulse shaper (SPS) as a tunable dispersion compensator.

The effects of fiber nonlinearity in Coherent Optical Orthogonal Frequency-Division Multiplexing (CO-OFDM) transmission, such as self-phase modulation (SPM) and cross-phase modulation (XPM), are a major concern. In this paper, we investigate the use of RF-Pilot (RFP) based nonlinearity compensation scheme in frequency domain to compensate for fiber nonlinearity in a coherent OFDM optical system. It shows that the RFP-based compensation scheme has superiority over a conventional pilot-based compensation scheme at FEC threshold.

When calculating nonlinear susceptibilities, a widely used two-level approximation in a sum-over states formulation is the exclusion of all but the ground state and one single excited state. With the goal of efficient optical frequency conversion, the basis of the two-level model is an assumption that just one excited energy level dominates, when determining the response of a nonlinear optical material. Naturally, any system that can be justifiably modelled as comprising just two energy levels affords numerous advantages, most notably calculational simplicity. However, caution is required; the two-level model can deliver potentially misleading results if it is applied without regard to the criteria for its validity. In a series of recent works, analytical results regarding the unsuitability of the two-level approximation have been proven. Ab initio computations of the hyperpolarizability for a class of merocyanine dyes have further demonstrated a drastic inaccuracy from not including higher energy levels in the calculations. In this paper, we report the results of our recent work testing the general validity of two-level calculations in nonlinear optics, constructed with a precise quantum electrodynamical framework as a basis for the theory. These new results show that, for the first-order dynamic polarizability, successive terms contribute progressively less to the final value of the tensorial components, guaranteeing convergence. In contrast, the values of second harmonic optical susceptibility components, similarly calculated, reveal that contributions from successive energy levels, often assumed to be diminishing, in fact fail to deliver the assumed convergence.

We investigate numerically the temporal and spectral characteristics of fixed-shape pulses, resulting from pulsating, erupting and creeping soliton solutions of a generalized complex Ginzburg-Landau equation (CGLE), which includes the third-order dispersion, intrapulse Raman scattering, and self-steepening effects. In general, the resulting fixed-shape solutions are asymmetric and chirped pulses. The interaction between such fixed-shape pulses is also investigated, and we show that a stable propagation is achieved, except when the pulses have an oscillating tail.­

Tapered fibres provide a unique means to manipulate pulse propagation for use in all-optical signal processing applications. Recently, we have demonstrated a new class of taper that is fabricated from our silicon core optical fibre platform. Owing to the high core-cladding index contrast, these silicon tapered fibres can accommodate large taper ratios over short millimetre lengths without introducing any appreciable loss. Such strong tapers allow for unprecedented control over the dispersion and nonlinearity parameters for the tailoring of femtosecond pulse propagation. Using numerical simulations based on realistic tapered fibres with micro to nanoscale core dimensions, we have shown that it is possible to exploit the longitudinally varying waveguide parameters for nonlinear pulse shaping in both the normal and anomalous dispersion regimes. In the normal dispersion regime, we have made use of a decreasing dispersion profile to generate linearly chirped parabolic pulses which allow for high power distortion-free propagation. Similarly, in the anomalous regime a decreasing dispersion profile can be used to compensate for the material losses to allow for soliton propagation, and even soliton compression to generate ultrashort pulses. Due to the broad optical transmission window of silicon, we anticipate that nonlinear pulse shaping in tapered silicon fibres and waveguides will find use not only in the telecoms band, but also extending into the mid-infrared for applications in the life sciences.

We theoretically and experimentally investigate a singlemode-multimode-singlemode (SMS) structure based on chalcogenide (As₂S₃) multimode fiber and conventional silica singlemode fibers. The experimental results show a general agreement with the numerical simulation results based on a wide angle-beam propagation method (WA-BPM). The chalcogenide fiber and silica fibers were mechanically spliced and packaged using a UV cured polymer with a low refractive index on a microscope slide. Multimode interference variation was observed by photo-induced refractive index changes resulting from both a localized laser irradiation at a wavelength of 405 nm and a UV lamp. Our result provides a platform for the development of compact, high-optical-quality, and robust photonic nonlinear devices.

The ability to control the speed of light on an optical chip is fundamental to the development of nanophotonic components for alloptical signal processing and sensing [1-7]. However this is a significant challenge, because chip-scale waveguides require very large changes in group index (Δn_g) to achieve appreciable pulse delays. Here, we use Stimulated Brillouin Scattering (SBS) to report the demonstration of on-chip slow, fast and negative group velocities with Δn_g ranging from −44 to +130, and delays of up to 23ns at a pump power of ~300mW and propagation length of 7cm. These results are obtained using a highly-nonlinear chalocogenide (As₂S₃) rib waveguide, in which the confinement of both photons and phonons results in strong interaction. SBS can be used to achieve controllable pulse delays at room temperature over a large wavelength and signal-bandwidth [5]. These results open up a new set of photonic applications ranging from microwave photonics [8] to spectrometry [4].

Electronic nonlinearities can lead to ultra-fast refractive index switching. This dynamic refractive index change can be used to shift wavelengths as well as to mix pulses of different center wavelengths. Due to its high refractive index silicon is suitable for tightly focusing light and generating high intensities required for such nonlinear effects, however high nonlinear losses in silicon (two photon absorption and absorption by free carriers generated via two photon absorption) limit transmission of high power pulses in silicon. Polymers and chalcogenide glasses have an improved nonlinear figure of merit (ration of nonlinear effect to nonlinear losses) and also don't show free carrier absorption. Due to acceptable levels of losses from generated free carriers, silicon organic hybrid or silicon glass heterogeneous structures offer to achieve high conversion efficiencies and large net gain in micro photonic devices, which can be used for wavelength conversion, parametric amplification and parametric oscillators, or for the generation of entangled photon pairs. We show both theoretical estimates and experimental results for four wave mixing conversion efficiencies in silicon hybrid and silicon heterogeneous structures.

Design, fabrication and test of an optofluidic device are presented. It is constituted of a circular waveguide crossing a fluidic channel integrated in a monolithic LiNbO₃ wafer. The fluidic channel is realized by precision sawing and the optical waveguide is induced by photorefractive beam self-trapping controlled by the pyroelectric effect. The self-aligning property of this latter writing technique allows both, efficient light coupling inside the channel and light collection after channel crossing. It is shown that the refractive index of a liquid present in the fluidic channel can be accurately evaluated by simple monitoring of the light transmitted through the waveguide.

We investigate the nonlinear propagation of intense Airy beams forming filaments in transparent media. We demonstrate the existence of stationary nonlinear Airy beams in a planar geometry. These beams preserve the intensity profile and the transverse acceleration of the Airy peak. We show that stationary propagation is sustained by a continuous energy flux to the main Airy lobe from its neighbors. For powers in the main Airy lobe exceeding a certain threshold, this stationary propagation regime becomes unstable. We extend our results to the 2-dimensional case: Airy beams with high powers in the main lobe reshape into a multifilamentary pattern induced by Kerr and multiphoton nonlinearities. The nucleation of new filaments and their interaction, affects the acceleration of the main Airy lobes. Experiments performed in water corroborate the existence of these two regimes.

We present the evolution of SCE associated with filaments due to the tilt of focusing lens under tight focusing geometries. Transform limited femtosecond (fs) pulses (800 nm, 45 fs, 1 kHz repetition rate) were focused in ambient air using three different focusing geometries f/#6, f/#7.5, and f/#12 corresponding to numerical apertures (NA) of 0.08, 0.06, and 0.04, respectively. The focusing lens was tilted from zero up to 20 degrees. The filaments decayed into two shorter parts through tilting of the lens and the separation between shorter filaments increased with increasing lens tilt, in tune with earlier reports [Kamali et al., Opt. Commun. 282, 950-954 (2009)]. The separation between the filaments matched well with the predicted distances due to astigmatism induced in loose focusing geometries. However the deviation increased as we moved to the tighter focusing geometries. The SCE spectrum demonstrated an anomalous behaviour. The SCE spectrum was suppressed at larger tilt angles of 12 - 20°. However at lower tilt angles, up to 8°, the SCE was observed to be same to that measured without any tilt of the focusing lens. This behaviour is predominant with tighter focusing geometries of f/#6 and f/#7.5, wherein the SCE was observed to be higher at 4° and 8° in comparison with that observed at an angle of 0°. Systematic study of the focusing lens tilt on anomalous SCE spectra and filament characteristics in the tight focusing geometry are presented.

We present the experimental investigations on the filament characteristics of sharply focused fs pulses (800 nm, 45 fs, 1 kHz) in air. Pulses with input powers in 3-12.2 P_Cr range were focused using three different focusing geometries f/#10, f/#15 and f/#20 corresponding to numerical apertures (NA) of 0.05, 0.033 and 0.025, respectively. The dynamics of filaments were observed via direct imaging of the entire reaction zone. The length of the filament has decreased with increasing NA from 0.025 to 0.05, while, the filament width has increased. For a given focusing geometry, the filament length and width increased with increasing power. However with higher NA, the length and width were observed to saturate at higher input powers. With the highest NA of 0.05 and higher input powers used in the current study, the presence of coherently interacting multiple filaments either resulting in a fusion or exchange of power.

We present the results on the electromagnetic (em) radiation emitted in the 70 MHz - 1 GHz frequency range from the laser induced breakdown of atmospheric air. Laser pulses (7 ns) from second harmonic of an Nd:YAG laser (532 nm) were used to breakdown atmospheric air to form plasma. During the plasma evolution and expansion, dipole moment is induced in the homonuclear molecules of nitrogen and oxygen (the main components of atmospheric air), which naturally have no permanent electron dipole moments. The RF spectra originating from the longitudinal oscillation of these induced dipoles was detected using the RH-799 broadband Diamond antenna. A spectrum analyzer (Agilent PSA E444A, 3 Hz to 50 GHz) was used to monitor and record the RF spectrum from plasma. By tuning the length of the antenna, lines corresponding to the different resonant frequency were observed at different laser energies. The total emitted RF energy was found to be increasing with the input laser energy up to certain input laser energy, beyond which emission properties were modified drastically. This was observed due to the presence of multiple breakdown sources due to the self-focusing of the ns laser pulses, modifying the collisions between the plasma electrons and eventually modifying the induced dipole moment in the detection range. The emitted radiation showed a specific polarization property associated with the input em radiation.

In this work, we experimentally demonstrate light-by-light polarization control for Telecom applications via a nonlinear interaction occurring in single mode fiber between a signal beam and a counter-propagating control pump wave. In particular, we observe an attraction and stabilization process of the state of polarization (SOP) of a 10-Gbit/s optical telecommunication signal around 1550 nm for either on/off keying (OOK) and non return-to-zero (NRZ) modulation formats. In a second section, we extend our device to 40-Gbit/s by experimentally combining an all-optical regeneration of both the polarization state and the intensity profile of a 40-Gbit/s OOK signal in a single segment of fiber. These experimental results confirm yet another fascinating way to all-optical control light features within optical fibers.

The generation of a broadband optical frequency comb with 80 GHz spacing by propagation of a sinusoidal wave through three dispersion-optimized nonlinear stages is numerically investigated. The input power, the dispersion, the nonlinear coefficient, and lengths are optimized for the first two stages for the generation of low-noise ultra-short pulses. The final stage is a low-dispersion highly-nonlinear fibre where the ultra-short pulses undergo self-phase modulation for strong spectral broadening. The modeling is performed using a Generalized Nonlinear Schrodinger Equation incorporating Kerr and Raman nonlinearities, self-steepening, high-order dispersion and gain. In the proposed approach the sinusoidal input field is pre-compressed in the first fibre section. This is shown to be necessary to keep the soliton order below ten to minimize the noise build-up during adiabatic pulse compression, when the pulses are subsequently amplified in the next fibre section (rare-earth-doped-fibre with anomalous dispersion). We demonstrate that there is an optimum balance between dispersion, input power and nonlinearities, in order to have adiabatic pulse compression. It is shown that the intensity noise grows exponentially as the pulses start to be compressed in the amplifying fibre. Eventually, the noise decreases and reaches a minimum when the pulses are maximally compressed. A train of 70 fs pulses with up to 3.45 kW peak power and negligible noise is generated in our simulations, which can be spectrally broadened in a highly-nonlinear fibre. The main drawback of this compression technique is the small fibre length tolerance where noise is negligible (smaller than 10 cm for erbium-doped fibre length of 15 m). We finally investigate how the frequency comb characteristics are modified by incorporating an optical feedback. We show that frequency combs appropriate for calibration of astronomical spectrographs can be improved by using this technique.

In this paper we report a two octave spanning supercontinuum generation in the range 750-3000 nm with a newly developed photonic crystal fiber. The fibre is fabricated using an in-house synthesized lead-bismuth-galate glass PBG08 with optimised rheological and transmission properties in the range 500-4800 nm. The photonic cladding consists of 8 rings of air holes with a fibre core diameter of 3 μm and a lattice constant of 2.2 μm. The dispersion characteristic is determined mainly by the material dispersion and the first ring of holes in the cladding with a filling factor of 0.68. The filling factor of the remaining 7 rings is 0.45 which allows single mode performance of the fibre in the infrared range. The fibre has a zero dispersion wavelength of 1490 nm which allows the use of 1550 nm wavelength as an efficient pump in the anomalous dispersion regime. The 2 cm long sample of photonic crystal fiber is pumped in the femtosecond regime with a pulse energy of 10 nJ at a wavelength of 1550 nm. A flatness of 5 dB is observed in the spectral range 950-2500 nm.

Optical frequency combs are a useful tool for measuring reference laser frequency whose uncertainty depends on the stability and accuracy of the reference clock. The relative uncertainty of the laser frequency measurements in the optical telecommunication band with the frequency comb technique is estimated around 10^-12. In this paper, we present the development and implementation of a filtering technique on an optical frequency comb based on an Erbium optical fiber oscillator using Brillouin scattering amplification. This filtering technique allows us to isolate and transmit frequencies generated by a stabilized optical frequency comb. This method has been developed for the remote comparison of frequency combs. Finally, we present the characterization of the optical frequency comb and its application to the calibration of high wavelength resolution meters in the optical telecommunications window. Measurements with uncertainties under the resolution of the own instrument were achieved using stabilized lasers at molecular absorptions. The result is a significant improvement of the measurement capability given by the current equipment.

The supercontinum generation has been achieved mainly by two different approaches, namely, with femtosecond intense pulses or using a continuous wave laser or larger pulses centered on the anomalous dispersion region. In order to improve temporal coherence, it has been suggested the introduction of a pulse seed or the propagation of both a large pulse pump and a small weaker continuous wave to control the soliton fission. Here we propose supercontinuum generation using a hybrid input, we pump with a continuous laser and copropagate a picosecond signal. We compare the bandwidth of the supercontinuum using only the continuous pump or the hybrid setup. Simulations of the generalized Schrodinger equation, using an adequate input-noise model to reproduce the spectrum of the continuous signal, are performed in order to investigate the supercontinuum generation in the optical communication window under different dispersion regimes.

We have developed a fibre-based source of "black light", a source that emits broadband ultraviolet radiation but only small amounts of visible light and no infrared light. We made this source by pumping a specially designed silica photonic crystal fibre with 355 nm light pulses from a Q-switched frequency-tripled Nd:YAG laser. Four-wave mixing and cascaded Raman generation combine in the fibre to provide a broadband continuum output that spans from around 350 nm to 390-470 nm, with the exact spectral width dependent on the pump power. We discuss the main limitations in terms of bandwidth and power due to temporal walk-off, fiber attenuation and solarization and we suggest simple solutions for further progress. This broadband black-light source could be useful for performing gas absorption spectroscopy or exciting various fluorescent proteins used in biological studies.

The microstructured optical fibers have been considered in this paper due to their unique nonlinear properties. These optical fibers have enormous potential and they are also unrestraint to tailor the design for obtaining promising dispersion properties. It has been observed that conversion efficiency significantly increases when nonlinear contribution to propagation constant is considered for phase matching. The phase matching have been obtained for even and higher order dispersion with the optical pump pulse conditions. The coupled mode theory along with nonlinear Schrödinger equation has been used to reveal the optical properties of telluride/phospho-tellurite hybrid microstructured optical fiber. The paper has been focused to investigate the effective index, pulse propagation intensity and quasi phase matching.

We design an ultra-compact low power all-optical modulator by applying dispersion engineered slow-light waveguuide in photonic crystal Mach-Zehnder interferometer (PhC-MZI) arms, which are infiltrated by optofluidic having high nonlinearities. Nearly zero dispersion regime brings us a 22-μm long PhC-MZI to operate as a modulator with an input power as low as 3 mW/μm. By attaching a coupling section about 3.36 μm long and inserting the light through a directional coupler with the lenght of 2.1 μm, losing power from the input port has been decreased.

We demonstrate an all-fiber broadband supercontinuum (SC) source with high efficiency in a single-mode high nonlinear silica fiber. The SC is pumped by the 1557 nm sub-picosecond pulse, which is generated by a homemade passively mode-locked fiber laser, amplified by an EDFA and compressed to 600 fs. The high nonlinear fiber used in experiments has the zero-dispersion wavelength of 1584 nm with low dispersion slope. The pump pulse is in the normal dispersion region and the SC generation is initiated by the SPM effect. When the long-wave band of the spectrum is extended to the anomalous dispersion region, the soliton effects and intra-pulse Raman effects extend the spectrum further. Meanwhile, the dispersive waves shorter than 1100 nm begin to emerge because the phase matching condition is satisfied and the intensity increases with increasing the pump intensity. The broad SC spectrum with the spectral range from 840 to 2390 nm is obtained at the pump peak power of 46.71 kW, and the 10 dB bandwidth from 1120 nm to 2245 nm of the SC covers one octave assuming the peak near 1550 nm is filtered. The temporal trace of the SC has the repetition rate of 16.7 MHz, and some satellite pulses are generated during the nonlinear process. The SC source system is constructed by all-fiber components, which can be fusion spliced together directly with low loss less than 0.1 dB and improves the energy transfer efficiency from the pump source to the SC greatly. The maximum SC average power of 332 mW is obtained for the total spectral range, and the slop efficiency to the pump source is about 70.3%, which will be lower when the peaks near 1550 nm are filtered, but is higher than those in PCFs. The spectral density for the 10 dB bandwidth is in the range from -17.3 to -7.3 dBm/nm.

Photorefractive nonlinear optical surface guided wave (SGW) excitation as a result of laser beams internal reflection from single-domain strontium barium niobate crystal (SBN-61) surface was demonstrated experimentally. We determined theoretically and experimentally SGW's transverse intensity distribution and recognized that SBN's biased dc electric field and background lateral illumination have forcible impact on SGW formation. For our opinion this experiment was the first when it was demonstrated that SGW stable stationary existence is limited by processes of transversal modulation instabilities (MI). MI drives SGW into an unexpected regime of propagation in which beam fragmented on to stochastic periodical pattern of bright spots. MI is aroused if biased dc electric field exceeds the threshold. Value of biased dc electric field and intensity of background lateral illumination determines spatial scale of the MI fragments.

Phthalocyanines, Porphycenes, and Corroles are macromolecules with large number of delocalized π electrons. The magnitude of response of these loosely bound electrons to short laser pulses determines their applicability in various applications such as optical limiting, optical single processing etc. A meticulous understanding of their performance using different pulses and at various wavelengths is indispensable to extract their accurate potential. Herein, we try to compare and contrast the nonlinear optical performance of these molecules in the ns, ps, and fs time domains. The nonlinear optical coefficients and figure of merits were estimated from the Z-scan data using different pulses over a range of input wavelengths. Ultrafast excited state dynamics of these molecules were studied using the pump-probe and degenerate four wave mixing techniques. A review of all the results obtained is presented.

Expanded porphyrins belong to the class of porphyrinoids, where the core of the porphyrin macrocycle is increased either by incorporating additional pyrrolic units, or by increasing the number of bridging carbon atoms from more than four, or a combination of both. The significance of these classes of compounds lies in their novel photophysical and nonlinear optical properties. Superior nonlinear optical coefficients are usually observed for aromatic expanded porphyrins with large number of π-electrons owing to their distinct structural features. In this regard, cyclo[8]pyrrole is unique, owing to its large planar 30-π core macrocyclic ring in its diprotonated state. Here, all the eight pyrrole units are directly linked to each other through their á-positions. Recently, we have synthesized, cyclo[4]naphthobipyrroles, a unique class of cyclo[8]pyrroles, where alternate pyrrole units are fused with naphthalene moieties. This adds more rigidity to the resultant cyclo[8]pyrrole while further extending the resultant π-conjugation. Herein, we present some of our results from the picosecond nonlinear optical studies of a â-octa-isopropyl-cyclo[4]naphthobipyrrole. The nonlinear optical coefficients were extracted from the Z-scan measurements. The values of two-photon cross-sections obtained for these molecules were in the range of 10⁴ GM.

In this work we present measurements of the switching of the Faraday effect in metal-organic compounds. Faraday rotation is the rotation of the plane of polarization of linearly polarized light under the influence of a magnetic field in the direction of propagation of the light. It is the magnetic equivalent of circular birefringence and is related to magnetic circular dichroism via the Kramers-Kronig transformation. The Faraday effect is used in optical isolators and magnetic sensors. Faraday rotation and magnetic circular dichroism spectra have been calculated and measured for various nanoparticles, nanocomposites, magnetic fluids and metal-organic complexes. These measurements and calculations indicate that it is possible to change the magneto-optical response by changing the state of the molecule, such as a change in protonation or oxidation state. The molecular environment also influences the magneto-optical spectra of metal-organic complexes and organic molecules. Thus it is possible to change the Faraday rotation spectrum by modifying the molecular environment or the molecule itself. We have measured the reversible switching of the magneto-optical response by these principles. This easily induced reversible switching opens the possibility of new devices such as switchable optical isolators.

Because the germanium native oxide constitutes a poor dielectric, building metal oxide semiconductors (MOS) gate stacks on Ge requires passivation of the interface between the dielectric and the Ge channel. Different approaches to perform this passivation are available: GeO₂ growth prior to high-k depositing, sulphur passivation, etc. The interface properties of these MOS stacks are important, because they determine the electrical properties of the whole structure. Dangling bonds introduce extra energy levels within the band gap, which results in a loss of efficiency in switching a MOS - field effect transistor on and off. Fixed charges near the interface enlarge the voltage needed for switching between on and off state as well. Hence, characterizing these interfaces is a key challenge in semiconductor fabrication. This can for example be achieved using Second Harmonic Generation (SHG) to probe the interface, because SHG is an inherent surface and interface sensitive technique. In this work, we present SHG as an promising surface and interface characterization tool for semiconductors for passivated germanium samples. Different SHG responses are shown for germanium samples with a sulphur passivated Ge or high-k dielectric on top of Si. We show that the oxide layer as such is not probed by SHG and that different bonds over the Ge/oxide interface result in a difference SHG response.

Magneto-optically active organic compounds are of great technological interest. In contrast to inorganic materials, used in most current applications, organic materials have the advantages of fast response times, easy processing, low cost and abundant resources of starting materials available. Conjugated organic molecules or polymers have been reported to be eligible candidates for exhibiting magneto-optical responses. As part of an ongoing search in our group for efficient magneto-optical materials, eight organic conjugated dyes were screened for their Faraday rotation responses. Based on the obtained preliminary results, it is expected that planar, efficiently pi- conjugated molecules have a higher chance for exhibiting significant magneto-optical responses. Further research will be undertaken to confirm this hypothesis.

In this work the possibility of laser overheating of light-absorbing surfaces of bulk carbon samples to incandescent temperatures with the use of a moderate-power Q-switched YAG-Nd³⁺ laser (wavelength 1064 nm, pulse duration 20 ns, power density 3-10 MW/cm²) was studied. We observed laser-induced incandescence (LII) of carbon surfaces and investigated its properties. When the surface was irradiated by a sequence of laser pulses, unusual changes of LII intensity were discovered in the experiments. Also significant nonlinearity in the dependence of LII intensity on the laser pulse power density was observed. The average temperature of irradiated surface was estimated by approximating the experimental LII spectrum by Plank's function and by computer simulations of laser heating of the carbon surface. For typical experimental conditions, the value of 2400 K was obtained. Both of the estimates of temperature are in a good agreement. The model, which is proposed to explain the observed effects, is based on the equation of heat conduction. Well-known thermal and optical properties of carbon are taken into account. The observed effects can be explained by essential nonuniformity of heating of rough surfaces and dominant evaporation of carbon from the tops of surface asperities.

We present third-order optical nonlinearities of Ag nanoparticles fabricated using a two-step ion exchange method. The nonlinearities are studied using the well-known Z-scan technique. In our experiments, we use a Ti-Sapphire laser source operating at 800 nm, which is far from the resonance of the Ag nanoparticles. The nonlinear refraction of these nanoparticles is studied using the closed aperture configuration of the Z-scan method. Contrary to expectations from previous studies for similar-sized nanoparticles, our nanoparticles possess positive nonlinear refractive index. The estimated nonlinear refractive indices are in the range of 10^-12 cm²/W.

We study Anderson localization of light in a photonic lattice in which the dimension is gradually changing from one to two. The influence of nonlinearity and disorder effects on Anderson localization in such a transitional system is investigated numerically. A sharp difference between localization in the linear and nonlinear regimes is demonstrated. In the linear regime, localization is more pronounced in two dimensions, whereas in certain nonlinear regimes it is more pronounced in one dimension. We also find that the localization in the intermediate cases of crossover is less pronounced than in both the pure one-dimensional and two-dimensional cases in the linear regime, whereas in the nonlinear regime this depends on the strength of the nonlinearity. We find two different localization lengths in the system with dimensionality crossover.

Special features of light-induced scattering of radiation (λ = 0.44 μm) with extraordinary polarisation in the SBN-75 photorefractive crystal are studied in detail and an efficient technique is proposed for exciting surface waves in this crystal. In the experiment carried out the efficiency of the surface wave excitation was ~ 30%, which is 50 times greater than that achieved earlier in exciting nonlinear surface waves in the optical region. The patterns of the near and far fields of the surface wave are presented. It is found that at small excitation angles (0-1.5°) the presence of a metal changes the character of arising surface waves. Using method of images for calculation of electrostatic fields a model is proposed explaining the peculiarities of light propagation close to the crystal-metal boundary.

New molecular design of obtaining molecular glasses has been developed by linking triphenylmethyl moieties to chromophore core by flexible C-C bridge. Compounds capable of forming stable amorphous phase with good optical quality have been acquired with increased chemical and thermal sustainability compared to the previously reported design. NLO activity of compounds has been measured after corona discharge polling. Compared to previously synthesized trityloxy fragment containing compounds increase of d₃₃ coefficient by up to 17 times was achieved for the same chromophore core containing compounds.

We demonstrate theoretically and experimentally that modulation instability leading to optical pattern formation can arise by using non conventional counterpropagating beams carrying an orbital angular momentum (optical vortices). Such a vortex beam is injected into a nonlinear single feedback system. We evidence different complex patterns with peculiar phase singularities and rotating dynamics. We prove that the dynamics is induced by the vortex angular momentum and the rotation velocity depends non linearly on both the vortex topological charge and the intensity of the input beam.

Reservoir computing has recently been introduced as a new paradigm in the eld of machine learning. It is based on the dynamical properties of a network of randomly connected nodes or neurons and shows to be very promising to solve complex classication problems in a computationally ecient way. The key idea is that an input generates nonlinearly transient behavior rendering transient reservoir states suitable for linear classication. Our goal is to study up to which extent systems with delay, and especially photonic systems, can be used as reservoirs. Recently an new architecture has been proposed¹ , based on a single nonlinear node with delayed feedback. An electronic¹ and an opto-electronic implementation^{2, 3} have been demonstrated and both have proven to be very successful in terms of performance. This simple conguration, which replaces an entire network of randomly connected nonlinear nodes with one single hardware node and a delay line, is signicantly easier to implement experimentally. It is no longer necessary to construct an entire network of hundreds or even thousands of circuits, each one representing a node. With this approach one node and a delay line suce to construct a computational unit. In this manuscript, we present a further investigation of the properties of delayed feedback congurations used as a reservoir. Instead of quantifying the performance as an error obtained for a certain benchmark, we now investigate a task-independent property, the linear memory of the system.

We present a widely-tunable, singly-resonant optical parametric oscillator, emitting more than 1 W in the region between 2.7 and 4.2 μm. Two configurations have been studied in order to improve the frequency stability and the linewidth of the OPO emission. First, we stabilized the signal frequency to a high-finesse Fabry-Perot cavity. Then, we locked both pump and signal frequency to the frequency comb generated by a NIR fs mode-locked fibre laser, linked to the caesium primary standard. With this last configuration we carried out saturation spectroscopy of several transitions belonging to the ν₁ rovibrational band of CH₃I, resolving their electronic quadrupole hyperfine structure, and determining the absolute frequency of the hyperfine components with a 50-kHz-uncertainty. An upper limit for the idler linewidth has been estimated as 200 kHz FWHM.